An unsaturated nitrile-conjugated diene-based rubber has been so far known as a rubber excellent in oil resistance, however, using only of this rubber had an inferior in weather resistance, especially in ozone resistance because a main chain has a double bond.
In order to improve the weather resistance, a rubber comprising an unsaturated nitrile-conjugated diene-based rubber and polyvinyl chloride (disclosed in JP-A-50-94063 and the like), a rubber comprising an unsaturated nitrile-conjugated diene-based rubber and a chlorinated polyethylene (disclosed in JP-A-57-119943 and the like) and a blend comprising an acrylic rubber and an ethylene-α-olefin-based copolymer (disclosed in JP-A-62-280244, JP-A-62-59650, JP-A-53-23342 and the like) have been known.
When the former rubber is used, oil resistance and weather resistance are excellent, however, containing a halogen causes to a releasing of a toxic gas by combustion, the use of a halogen has been restrained in recent years. Therefore, a halogen-free rubber excellent in oil resistance and weather resistance has been in demand.
In addition, when the latter rubber is used, weather resistance, particularly ozone resistance is excellent, but inferior in oil resistance. Thus, it can not be said that the latter rubber has a good balance to be excellent in oil resistance, weather resistance and mechanical properties.
Moreover, blending of an elastomer has provided new characteristics or has improved various characteristics, and a vulcanized rubber composition blended with an α,β-unsaturated nitrile-conjugated diene-based copolymer and an acrylate-based copolymer has been known (disclosed in JP-A-55-104332, JP-A-57-25342, JP-A-1-297451 and the like). However, it can not be also said that this rubber composition has a good balance to be excellent in oil resistance, fuel oil resistance, weather resistance and mechanical properties.
Accordingly, a halogen-free rubber product excellent in weather resistance, oil resistance and strengths with a good balance and a rubber composition that provides the same has been required.
An acrylic rubber is a copolymer of an acrylic acid ester as a main component and a monomer to form a crosslinking point. It has generally been known as a rubber that provides a rubber product excellent in thermal resistance, oil resistance and ozone resistance, and has been used as a molding material of an oil seal, an O-ring, a packing and the like. In recent years, accompanying with a higher performance of automobiles, required properties cannot be satisfied with ordinary levels of thermal resistance, oil resistance and cold resistance of rubber materials, and a development of a rubber having higher properties has been in demand. For example, since rubber parts are used at higher temperatures, a fuel oil-resistant rubber material excellent in thermal resistance has been required. Moreover, with respect to a seal material, it has been strongly required to improve thermal resistance, compression set and water resistance. Generally, a crosslinkable acrylic rubber includes a rubber using a monomer having active chlorine as a constituent or a rubber using a monomer having an epoxy group as a constituent to form a crosslinking point, however, a rubber by a monomer having active chlorine leads to a crosslinked material problematic in compression set, metal corrosion resistance and the like. A rubber by a monomer having an epoxy group had a low crosslinking rate, being problematic. Various crosslinkable monomers other than these monomers have been studied, however, when a conjugated diene monomer such as butadiene and pentadiene are used, a crosslinking reaction occurs during polymerization and no good polymer is obtained.
An acrylic rubber from an acrylic acid alkyl ester as a main constituent is quite inferior in fuel oil resistance to a nitrile rubber, a fluororubber, a hydrin rubber, a hydrogenated nitrile rubber and the like, and it could not be used in a portion in contact with fuel oil.